The cooling jacket for cooling a heating element includes: a main portion including plural fins for defining a passageway through which a coolant flows; and a cover covering the main portion. The cover portion abuts the ends of plural fins to be attached to the main portion. Technologies relating to a cooling jacket are disclosed in Japanese Unexamined Patent Application Publication Nos. 2006-324647, 2001-35981, and 2009-206271.
As mentioned above, the cooling jacket is made of two members. Therefore, a gap may be generated between the ends of the fins and the cover portion. When the coolant flows through the gap between the ends of the fins and the cover portion, the flow rate of the coolant which should originally flow between the fins may decrease. Accordingly, the cooling efficiency may decrease.